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degradation principles mud fertilises the sea and the marine ecosystems recycle these nutrients Soil erosion is natural and the sediments and nutrients it carries to the sea help fertilise the sea, resulting in plankton blooms which are the basis of the main food chains in the sea. Sediments disperse across the continental shelves, leaving sand to replenish beaches, and much finer silt on the shelves for the 'sea soil' which is important in recycling nutrients. The fine clay particles disperse down the continental slopes and they are very slowly (hundred millions of years) recycled by sea plates moving under the continental shelves. A small and sustainable loss of soil from the land makes room for the fertility locked in deeper layers to reach the surface, and has a benefit here too. But too much loss not only disturbs the balance but can also cause very serious degradation on both the land and in the sea. The diagram shows how mud (from loams), flowing from the land into the sea, is split into its three main components, sand silt and clay. The heavy sand particles are deposited close to the shore and these eventually feed the beaches and dunes. Silt disperses to the centres of the continental shelves and the ultra-fine clay particles in deeper water close to the continental slopes. In contact with salt water, both silt and clay release their nutrients (pink) which fertilise the plant plankton (green). Wastes are recycled by bacteria in the water and in the sea soil, to produce new nutrients and these are recycled repeatedly before they are lost to the open ocean.

If soil loss on land exceeds that of soil production through weathering and subsequent incorporation into the top soil, the soils become thinner, less fertile and less capable of storing moisture. The vegetation thins and eventually soils are insufficiently covered against the onslaught of heavy raindrops. The loss of soil now accelerates beyond control and eventually bare rock remains. Many places in the world, are progressing along this path of accelerating soil loss, also along coasts. The diagram shows how soils degrade in the process of being used for agriculture. Notice the amount of carbon held in soil organisms and humus and how this is lost gradually, almost unnoticeably. Then suddenly comes the point of no return, where the top soil disappears suddenly, with rapid loss of the loams underneath (mud). Before this happens, additional fertilisation combined with the planting of forests can still halt this process. But at our shores which have been ravaged by possums, this is a tall order, as these are steep while losing their coastal vegetation.

It has long been thought that the main component of erosion comes from the very visible slips, gully erosion and sheetwash (water flowing over land). But recent research has shown that the main loss of soil comes from the direct impact of rain drops on bare soil. This effect is rather acute, as increasing the size of a raindrop five-fold results in a release of 500 times more energy. Understandably, the most damage is done during the heaviest rains. All over the world the intensity of rains is increasing, and here in New Zealand we are witnessing torrential rains as never seen before. As a result, the amount of mud washed into the sea is increasing rapidly (my estimate: doubling every decade). For marine organisms that have evolved in the cleanest of coastal waters, this is a disaster of highest magnitude.  Here in New Zealand we do not have a reliable system for measuring the accumulative amount of sediment discharged to the sea. A simple method like placing sediment traps on all wharves, has never been thought of.

accumulation of coastal nutrients The nutrients above the continental shelves are mainly contained in the bodies of living plant and animal plankton as these move with tidal and ocean currents. It was once thought that sea currents cleanse the continental waters sufficiently, but a number of physical mechanisms herd nutrients back onto the shelves. The diagram shows how the sea winds towards the land are stronger than land winds, and the waves they produce are also much larger. This pushes a surface current towards the shore, and with it, the shallow plankton. Coastal currents corkscrew as they flow along the continental margins, pushing deep nutrients back onto the shelves. They also produce eddies that push plankton organisms and their nutrients back to the continental shelves. These three mechanisms conserve the productivity of the continental shelves, reducing fertility losses to the open ocean. Satellite images of chlorophyll (= the green plant matter for photosynthesis) confirm sharp boundaries at the continental shelf margins.

Many sources of pollution are point sources, as pollution is released at points along the coast, such as the mouths of rivers and estuaries. These pollution plumes flare out as tidal and ocean currents transport them along the coast, extending the damage to the coastal zone over a wide area. It has been observed, for example, that the pollution from Hamilton's Waikato River and Auckland's Manukau Harbour travels north, then around North Cape to go south again, causing damage to the Parengarenga and Houhora harbours, hundreds of kilometres away. One finds places far away from population densities still highly polluted by them.
 
 

the nutrients in shortest supply Plankton does not bloom just because nutrients and sunlight are available. Diatoms, the main food source in the sea, require silica for their shells and also iron, which are in short supply in clear salt water. But these two minerals are amply provided for by mud/clay since clay is an aluminium-iron silicate. Thus an inflow of mud can lead to a sudden plankton bloom that uses the already available nutrients. People often blame artificial fertiliser for problems in the sea but one needs to distinguish between flatland fertilisation and that of hill country. The first uses an excess in nitrates which leach quickly, being detrimental to freshwater ways and ultimately the sea. Hill country fertiliser uses no nitrates, little phosphate but much lime, potassium and sulphur. These components are readily available in the sea while phosphate binds firmly to clay particles. As a result, the threat from hill country is not from fertilisation but from erosion, which supplies the missing nutrients of silica and iron and the natural fertility locked up in clay. Ironically, this threat can be mitigated by fertilising aimed at improving soil cover. Since fertiliser subsidies were abolished in 1986, aerial topdressing declined sharply, such that the hill country is now insufficiently fertilised. It explains the sudden appearance and steep increase in marine degradation since 1987. The runoff from both types of land produces everything the plankton needs to bloom violently. Please note that the density of a plankton bloom depends mainly on the nutrients in shortest supply and will vary remarkably.

 

El Niño - La Niña cycle But there is another mechanism at work, that of the El Niño cycle. Contrary to what scientists claim, this is a slow and predictable cycle of about ten years during which the Pacific gyres (= circular currents) speed up and slow down. In the El Niño phase currents are minimal, resulting in warm water amassing in the tropics (coral bleaching and hurricanes) while temperate seas become cooler. The cleansing currents around NZ also diminish, resulting in fertility building up in our coastal seas. During the El Niño phase (1982-1983, 1992-1994, 2001-2005) excessive plankton blooms are experienced and cold water because less warm water reaches NZ. Degradation in the sea thus has two components: a gradual worsening superimposed on a ten year cycle.

Longer than usual periods of cold water are experienced by marine creatures as if the summer never came, and with it the chance of successful recruitment. Remember that the difference between summer and winter spans a range of 6ºC: 2 for winter, 2 for summer and 2 for spring and autumn inbetween. A two degree variation in temperature thus equals one season. Particularly for warm water species (snapper, kahawai and various jacks) the chance of successful recruitment decreases rapidly as the ratio of warm years over cold years does (e.g: nine good years in ten 9/10=0.9 versus three good years in ten 3/10=0.3). Thus spawning success can decrease rapidly below what we can imagine.
A decrease in temperature may also be decisive on grazing fish (and other creatures) whose digestive enzymes restrict their ranges. It could also affect growth of other species where these habitually seek shallow warm water to increase their digestive rates (and a sense of wellbeing), perhaps also necessary for successful spawning. Likewise an increase in temperature can affect species in their northernmost ranges.
 

plankton feeds and kills The dissolved nutrients from mud become available for the plant plankton which converts carbondioxide into carbohydrates and other building blocks of life, using the energy from sunlight. Because the phytoplankton organisms are so small, they can be 'grazed' only by small organisms. These are predated upon by ever larger ones, forming the ocean's food chain in many levels (trophic cascades). But invisibly, a large and very active component of the ocean consists of decomposers, suspended in the water as bacteria and viruses, and also living in the sea soil. These decomposing organisms are not friendly to living organisms (and to one another), threatening them with infections and decay. Just imagine what it would be like to be surrounded by sea water containing both one's food and excrement, and to breathe it as well. This concept has led to the plankton balance hypothesis (read this very important chapter first) which reminds us that plankton has two opposing aspects: that of feeding and killing. Organisms in the sea have evolved to live in the balance between the two - some in clear waters, others in more polluted waters. Should the balance change, organisms will die either for lack of food or for an excessive risk of infection. This alone explains mass mortalities and other loss of life as the concentration of plankton increases or decreases. In case of excessive rot (= dying organisms), the decomposers usurp most of the solar energy, and the plankton can suddenly become a potent killer, although not being poisonous.

One reason that decomposers are so influential, is that decomposers are the only ones connecting all trophic levels in an ecosystem.

In 2005 we discovered a method to measure the activity of the planktonic decomposers (read the DDA chapter) and this showed us that the decomposers can suddenly take over, thereby reducing the plankton's food value while increasing the risk to life. Plankton can suddenly turn from feeding to killing.
 
 

decay kills others Those who have saltwater aquariums will have found out that decaying organisms render the whole aquarium unhealthy because of the sudden increase in decomposing bacteria and fungi. In the open sea this is no different. A storm may remove large numbers of seaweeds from the rocks they grew on. Once these seaweeds decay, other organisms may die because of this (usually in a tranquil corner). A kelp forest which remains insufficiently grazed through the absence of grazing fish or snails, produces rotting leaves which affect the health of other organisms. Plant plankton which is insufficiently grazed by zoo plankton will die and cause decay in the entire water column, with unpleasant side effects. Organisms of decay are thus potent indicators of degradation. The sea soil could well be a potent source of poisons. When stirred by large storms, the otherwise locked up decomposers of the sea soils are released into the shallow waters of the continental shelves and with them poisonous substances like ammonia (NH4) and hydrogen sulphide (H2S). It is not known whether this effect is causing enough harm to be important.

 

symptoms are rare Symptoms of disease will be visible mostly on long-lived animals and plants because short-lived ones die soon from natural causes. It so happens that infections to the underwater world spread and kill quickly, leaving little chance of recovery. Because the period of visible symptoms is so short relative to the longevity of the organism, the symptoms may remain unnoticed or their seriousness underestimated. For instance, a male sandagers wrasse aged 15 years on average, while dying within two weeks of showing symptoms, is not likely to be seen, as the chance of encountering one is 1/(15x20)=1/300. One needs to meet 300 sandagers wrasses to meet one diseased one, even though the disease may be a major cause of its decline. Thus disease symptoms must be weighted (multiplied) with the longevity of the organism.

f046121: this male sandagers wrass (Coris sandageri) is in an advanced stage of a fungal infection that soon will break through to its brain and cause it to swimm erratically, as aquarium studies have shown. It takes about 2 weeks for the visible stage of this infection, reason why it is rarely seen even though it may be the cause of widely spread deaths. Poor Knights marine reserve 2005.

f046133: this grey nipple sponge (Polymastia fusca) has a bacterial infection that will slowly dissolve it and dislodge it from the substrate, which takes about 4 weeks. Aged about 4 years, and dying within 1/10th of a year, makes the chance of seeing these symptoms about one in 40. Poor Knights marine reserve 2005.

degradation is far worse than fishing The web of ecological relationships is not shaped like a fishing net with equal nodes and rungs, but like a pyramid with the main relationships following the flow of energy towards the top. There are influences downward but these are necessarily much smaller. The diagram shows this pyramid with the producers at the bottom and commercial fish species at the top. Each successive tier of this cake is about ten times smaller than the one beneath it. Thus fishing mainly takes a bite out of the small top of the pyramid (typically 0.1-0.01% of the total biomass). By contrast, degradation affects mainly the bottom tiers of the pyramid and in doing so, also all dependent tiers above. What fishermen see is a decline in fish, which they then attribute to overfishing, but in reality it is caused by direct kill (fish), kill of sensitive fish larvae, and a reduction in food (zoo plankton). This makes the impact of degradation far worse than that of fishing, to such extent that marine reserves do not help at all even where only a small degree of degradation exists.

causes, agents and effects This diagram shows how threats from human activities, affect the sea. It is a complicated web of causes and effects. On left in blue the main human activities. In the centre in brown and green the agents, and on right their effects on the sea. The main threatening activities are: urban development: as soil is shifted and laid bare, much of it washes away into the sea, up to 6000 times natural rate! roading: the cutting of roads and leaving them bare causes much erosion. The tar-seal does not absorb moisture but causes unimpeded runoff. farming: the lowlands are productive and overfertilised such that much fertiliser is washed out of soils, reaching the sea. By contrast, the highlands are underfertilised, resulting in loss of top soil and severe erosion. Much of our country has been denuded carelessly. Ploughed lands pose a very high risk of nutrient loss, soil loss and overfertilistation. sewage: sewage is a very balanced, almost perfect fertiliser. Where populations of people live, it forms the number one threat to the sea, killing organisms outright or by dense plankton blooms. Animal wastes from farming also reach the sea. It is estimated that 50 million sheep plus 8 million cattle amount to a waste equivalent of 200 million people, but at least half of it recycles on the farm. industry: many non-biodegradable chemicals and minerals originate from industrial processes, and many find their way into garbage dumps from which they can leak into the sea. Some marine organisms are very sensitive to these, whereas others accumulate them. Because these chemicals can be measured easily, scientists have focused unduly on their potential threats which are very small compared to that of degradation. fishing: when people fish the sea, they take life, which kills mature organisms. Fishing is a form of predation of which the sea has many, but when overdone, it can impair the functioning of ecosystems. Fishing can kill non-targeted species as bycatch, including juvenile fish, sea birds and sea mammals. Nets can damage sessile life and change the sea soil. However, fishing alters only a small part of the whole ecosystem, typically no more than 1-3%. To say otherwise, is like saying that shooting the bears destroys the forest.

• nutrients: when in the right concentrations, cause dense plankton blooms which can: obscure light, killing plants + become infectious, killing plants and animals, particularly those with thin skins like fish larvae + cause plankton toxins that are extremely toxic to most animal life and humans.
• poisons: poisons from human activities and plankton blooms can accumulate in organisms, killing slowly or causing changes such as poor reproduction. They consist of industrial chemicals + agricultural chemicals and pesticides + heavy metals + plankton toxins.
• decomposing bacteria: recent discoveries with the DDA have shown that eutrophication can cause decomposing bacteria to increase substantially, causing deaths from infections. Decomposing bacteria kill phytoplankton, zooplankton and fish larvae and ultimately also long-lived organisms.
• debris: arises from carelessness but is usually inert and of little consequence to sea organisms. Some birds or sea mammals may become trapped. For this section it is of too little relevance.

the slippery downslope In nature the relationships between causes and effects are not necessarily linear. Particularly many biochemical reactions have an optimum outside which the effect diminishes. Eutrophication which is the overnourishment of rivers, lakes and the sea, has such an optimum (see diagram). When there are no nutrients, life cannot exist, so a certain amount is needed. When this amount is doubled, life responds likewise by doubling growth and production (A). But soon an additional amount of nutrients does not produce an increase in growth, and the optimum is reached (B). At this point, the excess in nutrients is neither beneficial nor harmful. But when it is increased further, growth diminishes and organisms display signs of illness or stress (C). Here eutrophication begins. If nutrients continue to be increased, death soon follows (D). Compare this with the requirements of a pot plant: too little nutrients or water is harmful, and too much of it also.

loss of light kills First we need to become familiar with the processes of degradation, one of which is shown in this diagram. On left a rich community in clear water. On right a severely degraded community in murky water. Loss of light clearly affects plants such that they can no longer grow deep. In severe cases only seaweeds tolerant to low light conditions survive. Observations show that they also need to be more tolerant to sedimentation and bacterial attack. Thus loss of light, suffocation by mud and being killed by disease organisms, are almost inseparable and usually come together. The lower boundaries of seaweeds are usually due to lack of light. In such places the plants can just survive, their energy budgets teetering between gain (in light) and loss (in darkness). As a result, such plants have little food value and are unattractive to feed on. They also have fewer reserves to fight infections and infestations. It is here that the first signs of degradation are found. The lower boundaries are worth taking note of since they are a direct measure of the average water quality. Degradation of water quality is first noted by the absence of young plants where old plants form an open canopy. The ratio of old over young organisms furthermore gives an idea of whether things get better or worse.

water movement saves One of the reasons people fail to notice degradation is because they do not go deep enough. Where the water is in constant movement, such as near the surface, mud and suffocating organisms cannot settle out (but toxins still have their effect). A similar place is found close to the bottom where sand is moved around, cleansing sessile organisms by its abrasive action. Degradation is most severe in tranquil and sheltered places, particularly inside caves. Note that the gradients discussed before provide a rich range of 'natural experiments' from which ecological conclusions can be drawn. The depth of the sand is a direct measure of the strength of long waves, which are the ones causing natural damage to the reef. This kind of damage is of a mechanical nature and can easily be recognised.

All this means that degradation, once it sets in, progresses quickly. It also means that the gradient from clear to dirty water has a very progressive effect on the environment!! And contrary to intuition, that the most profound effects of degradation are found in places with usually clear water!!
 
 

one dies only once Death is quite a profound effect. An organism may get infected or stunted but still has a chance of recovering, even being capable of reproduction. But death is final and irreversible. Missing organisms change their environment by leaving space for others and by affecting the lives of others. A one-off disaster has more profound consequences than a run of good years. Thus missing organisms and vacant territory are profound indicators of stress.

 

growth is slow, death is sudden Organisms grow slowly, often having to consume their bodies' weight many times. Populations also grow slowly. But death ususally comes suddenly as it happens in predation and through natural disasters. As a result, a single disastrous event will take many years to recover. Thus recovery from a disaster happens much more slowly than the disaster's immediate impact. When disasters happen more frequently, their lasting effect degrades the environment quite profoundly.

 

one's surface area shrinks with age Bacterial attack happens over an organism's entire surface, and is counteracted by the organism's self defence and reserves, which are proportional to body weight or volume. Assume for a moment a spherical fish whose surface area is given by 4 x pi x r x r and whose volume is given by 0.75 x pi x r x r x r  where r is the radius or size of this fictitional organism. The ratio between the two (= 5.33 x r ) is a measure of an organism's sensitivity to bacterial attack, and this grows proportionally as the organism grows. It is not unusual for a marine organism to grow from 1mm to 50mm (50-fold) in its first year and 1000-fold over a lifetime. Thus the larvae of marine organisms are much more sensitive to bacterial attack than their adults. Note that a spherical organism has the most favourable (smallest) ratio of surface area to volume but fish larvae which are thin and elongated, have the worst possible ratio. This explains why recruitment failure is an early symptom of degradation.

 

everything is connected Degradation does not only leave empty space<center>,<object data="../../sfmenu.htm#top" type="text/html" width="750" height="80"></object></center> but since everything is connected, also causes new phenomena. For instance, a mass mortality of predators shows up in an excess of young prey. Mass mortality of schooling fish shows up in undamaged jellyfish which otherwise would have had their gonads (eggs) eaten out. As a consequence of an unusual event, other unusual phenomena will happen later, which confirm the original observation. Thus observation cannot stop once the effect is over, but must continue well into its aftermath.

The decline of scallops (Pecten novaezelandiae) in Whangaroa Harbour initially increased fishing effort, with consequent damage of the sea bottom, but eventually reduced it as people gave up. As a result, the carpet fanworm has made an impressive come-back, even though the underwater habitats there have been ravaged by degradation.
 
 

f040009: carpet fan worms have made a come-back in Whangaroa Harbour due to the decline in scallop dredging but they are now threatened by rapidly deteriorating water quality.

f042126: the fluffy sediment layer shows that it is not being grazed. Although sediment is a strong indicator, the vast amounts of vacant territory are even more meaningful.

• not being able to observe the marine environment, such as diving for sport, food and work (includes research).
• not being interested in observing marine life and how it degrades, such as diving for fun, for photography, for food.
• unfamiliarity with marine organisms and their functions in the environment. One needs to know what lives where and why, and who eats what and how long they live for, and much more.
• unfamiliarity with ecological limiting factors like exposure, shelter, shading, niches, discontinuities in habitat (cracks, sand, slope/aspect), and so on. One needs to know how the sea differs from the land (Read biodiversity/marine) and what it means to live in the sea.
• not being able to dive where and when one wishes, using one's own boat, in good and bad conditions, all places, all habitats, all seasons.
• not being able to record the environment on photos which can stimulate the mind afterwards while providing an excellent record.
• not knowing the indicators of change: since it is impossible to see directly what is no longer there, one has to learn to see indicators of change.

One of the main recurring mistakes is that people fail to understand the differences between land and sea, and automatically make assumptions that are not valid. It is important therefore, to read the chapter on biodiversity and the introduction to marine habitats and read them again in order to get a good feel for the many important differences. If you want to test your new-found knowledge, study the Frequently Asked Questions about marine reserves as well.